The manufacture of flexible, thin film solar modules is often carried out by a roll-to-sheet process in which a plurality of photovoltaic cells are provided along the length of a roll of a web (viz. in the web direction) so that they are spatially separated from one another and the web so provided is cut into a plurality of sheets (or modules) each containing one of the photovoltaic cells.
In this process, the plurality of separate photovoltaic cells are formed by providing a plurality of separate bottom electrodes in discrete areas on the web along the web direction.
The bottom electrodes may be deposited using, for example, printing techniques such as screen printing, ink-jet printing, gravure printing or intermittent printing or by vacuum deposition using a mask.
Preferably, however, the plurality of separate bottom electrodes is provided by vacuum deposition of a bottom electrode layer which is continuous along substantially the whole of the length of the web and patterning that layer by etching or by mechanical or laser scribing along the web direction.
The patterning may be followed by providing one or more active layers over each of the bottom electrodes and a top electrode over each of the one or more active layers. The top electrode may, however, be a top electrode layer which is continuous along substantially the whole of the length of the web.
Of course, the patterning may be carried out after providing one or more active layers over the bottom electrode layer and a top electrode layer over the one or more active layers each along substantially the whole of the length of the web.
In that case, the patterning may provide separate top electrodes along the length of the web instead of or as well as separate bottom electrodes along the length of the web.
In any case, the cutting of the sheets from the roll is in the gaps between separate bottom electrodes and/or top electrodes and the individual sheets are normally encapsulated to protect the device against the ingress of oxygen and/or water by laminating between a backing sheet and a cover sheet.
In one case, a continuous top electrode is provided along substantially the whole of the length of the web by thermal evaporation and a plurality of top electrodes formed along the web direction by laser scribing. The scribing provides for spatial and electrical separation of the top electrodes by removing electrode material in parallel lines across the direction of the web. The cutting of sheets from the roll is carried out in the area between the parallel lines and is followed by encapsulation.
Of course, the one or more active layers include a photoactive layer and each cell has at least one electrode which is substantially transparent. The one or more active layers between the photoactive layer and the transparent electrode layer are also substantially transparent.
The manufacture typically provides a solar module having a number of parallel photovoltaic cells. These photovoltaic cells are formed across the width of the web (viz. across the web direction) in a similar manner as the spatially separated photovoltaic cells so that all the photovoltaic cells across the web direction are connected in electrical series.
In one arrangement, the top electrode of each photovoltaic cell contacts the bottom electrode of an adjacent photovoltaic cell so as to provide for electrical conduction between the connected cells. Bus bars are also be provided on the web adjacent to the first and last of the connected cells prior to the cutting of the web or by fixing to a sheet before or after its encapsulation.
The above-described methods suffer from a number of disadvantages that make the manufacture of these devices somewhat inflexible and expensive.
One disadvantage is that the length of a module is defined on the roll by the gaps provided between separate bottom electrodes and/or top electrodes. After cutting and encapsulation, the length of a particular module cannot be changed and the installation of the module is restricted to its predetermined use.
A further disadvantage is that the printing of the top electrodes is complicated by the choice of an appropriate ink. The available inks typically provide layers which are either too thick and/or too costly. They are, in any case, often based on solvents which are difficult to fully remove—which can compromise device performance. Further, they do not typically offer any barrier to the ingress of oxygen and/or moisture to the device.
Another disadvantage is that the lamination of the individual sheets cut from the roll requires specialised and expensive sheet to sheet (or sheet to roll to sheet) lamination equipment.
Background information can be found in U.S. Pat. Nos. 5,637,537, 5,385,848, and 5,202,271.